1. Field of The Invention
The present invention relates to fiber gypsum board (FGB) and composites and the method of manufacturing the same for use as building materials. More particularly, the invention is directed toward a fiber gypsum board and composites that can have a more variable density, and have greater strength. The invention further relates to novel methods, systems, and apparatus for manufacturing FGB and composites.
2. Description of Prior Art
It is well-known that conventional gypsum wallboard is typically manufactured from a plaster slurry which is put between two layers of paper.
In the conventional method, a wet slurry of gypsum is poured between two layers of paper and the slurry is allowed a certain amount of time to set up. In gypsum wallboard, the two layers of paper contain the slurry and provide the strength required in installation and use. The wallboard is cut into discrete lengths to accommodate subsequent handling and then dried in heated dryers until the board is completely dry.
The bending strength of the board depends on the tensile strength of the paper; while the gypsum serves as a "spacer" and accounts for fire resistance and moisture absorbing and moisture releasing activities. The static properties are limited, and the surface treatment and the joint filler system are determined by the paper.
There have been some efforts to arrive at a process for making gypsum fiber board by a slurry process. There are examples of dry and semi-dry processes disclosed in U.S. Pat. Nos. 3,737,265 to Schafer et al.; 4,328,178 to Kossatz; and U.S. Pat. No. 3,233,368 to Baehr et al.
Prior art processes which involve the moistening of mixed fibers and plaster have presented significant limitations and problems. The mixture of the fibers with water often results in the creation of clumps or balls of wetted fibers that are stuck to each other. Such balled fibers do not mix well with the gypsum and significantly reduce the strength of the resultant board and produce uneven and rough surfaces. To the inventors' knowledge, ball-free moistening and subsequent mixing of the moistened fibers, such as waste paper fibers, with plaster has so far not been commercially acceptable. Fire regulations often require a low fiber percentage in the finished board. As this percentage decreases, however, the moisture content which has to be applied to the fibers increases, thereby amplifying the balling effect. For example, to provide a board with the proper strength, a board having a fiber percentage of 22% of the finished board requires 150% by weight of water to 100% fibers, if the fibers are to carry the water for setting the plaster. In the prior art processes, such a high ratio of water to fiber results in balling.